From: Tom Lane <tgl@sss.pgh.pa.us>
To: Laurenz Albe <laurenz.albe@cybertec.at>
cc: Dominique Devienne <ddevienne@gmail.com>,
        Adrian Klaver <adrian.klaver@aklaver.com>,
        "David G. Johnston" <david.g.johnston@gmail.com>,
        Igor Korot <ikorot01@gmail.com>,
        "pgsql-generallists.postgresql.org" <pgsql-general@lists.postgresql.org>
Subject: Re: Fwd: Identify system databases
In-reply-to: <2dffe860b085b927726a052bcfe16ede704ab923.camel@cybertec.at>
References: <CA+FnnTxab=JyE0DZkfL4Z2MK8RvvTud9MZiNenD45AoV_t2Mxg@mail.gmail.com> <CAKFQuwYaDXuuDoEaad5sYW97pRS_FJnmfZCwY3FojnDOdfXc9Q@mail.gmail.com> <CA+FnnTzwmMTNymgPuiF4CLfa6YO+HBRx4Qy5_B_KDw1oNpiukw@mail.gmail.com> <CA+FnnTyWMXPEVAwNNDnCVDfmTFNHdDfffiF5vLioxyTv8Jmq0A@mail.gmail.com> <817abeac-d628-4279-bfef-9e1e3aa1884b@aklaver.com> <CAKFQuwbkQTbUwA4c6LFOMUWX5ojQY8DpKPQRh+xoe4VZABPWfw@mail.gmail.com> <25b6cd49-f871-47fe-bf3b-5416637736ca@aklaver.com> <CAKFQuwYpY7urAHuns26cw=9TKTZJU4JdVBrXWoSH_nHfZ_s3Ww@mail.gmail.com> <bcae9b4b-a85e-4fc7-8e70-5a98c5e5ff28@aklaver.com> <f5612b59b0a82bee2bf28efd314ac338bbc4c6b5.camel@cybertec.at> <CAFCRh-_uEazAHjSz1WvL2STbR857V7E9YtkdwRO5xNNHLy2Ykw@mail.gmail.com> <2dffe860b085b927726a052bcfe16ede704ab923.camel@cybertec.at>
Comments: In-reply-to Laurenz Albe <laurenz.albe@cybertec.at>
	message dated "Wed, 16 Apr 2025 14:30:27 +0200"
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Date: Wed, 16 Apr 2025 10:39:14 -0400
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Laurenz Albe <laurenz.albe@cybertec.at> writes:
> On Wed, 2025-04-16 at 10:09 +0200, Dominique Devienne wrote:
>> Authentication is cluster-wide, not DB specific, so I'd welcome a way t=
o connect
>> to the cluster, not a specific DB, and introspect shared-objects,
>> including databases
>> I'm allowed to connect to, which could be an empty list.

> It is deep in the DNA of PostgreSQL that you always have to connect to
> a database, unless you establish a replication connection.
> I am surprised that you perceive that as a problem or limitation.

That isn't going to change, and here's why not: a lot of the critical
catalogs are per-database not shared.  You aren't going to get
anywhere "introspecting shared objects" when you don't have a copy of
pg_class with which to find the shared catalogs, nor a copy of pg_proc
with which to look up index access method support procedures, etc etc.

You could imagine making up some mini-database that is somehow
forbidden from gaining any user-defined objects and then using
that, but I fail to see why that's a better idea than the
approach we use now.  Not being able to use any user-defined
functions or views seems like a pretty huge handicap.  And this
hypothetical new mini-database *would* be a special snowflake
in a way that none of the existing ones are, in that the system
would have to prevent actions that are perfectly okay in any
other one.  I don't perceive that as a good thing.

(You can, of course, speculate about some major rearchitecting
of the system catalogs that would make this situation different.
I doubt that's going to happen at this point, though.  There's
too much stuff that's dependent on how things are now.)

			regards, tom lane